A common hinge structure is used between a connecting rod and a bed leg rod of an existing hospital bed, where the longitudinal displacement of the bed leg rod during the folding and stretching thereof cannot be compensated, and the longitudinal position of a ground-touching end of the bed leg rod relative to the hospital bed will be changed. This results in the movement of the whole hospital bed. Because a hospital bed is always placed with one end pressing against a wall, bed legs away from the wall are normally forced to move backwards, with continuous vibration. This phenomenon generally makes a patient uncomfortable. Especially for a critically ill person whose body is full of various cannulas, dragging caused by the movement of the hospital bed may lead to serious consequences and affect the rehabilitation. However, for various reasons, the hospital bed must be able to be lifted and lowered according to specific requirements of a medical treatment. It is always a difficulty in the art to reduce the displacement of the bed legs in a process of lifting or lowering, thereby maintaining the stability of the gesture and position of a patient.